Bovine babesiosis

Previous Authors: A J DE VOS, D T DE WAAL AND L A JACKSON

Current Authors:
P J ROLLS - Principal Veterinary Officer, BVSc, MVS, Tick Fever Center, 280 Grindle Road, Wacol, Queensland, 4076, Australia 
P D CARTER - Principal Veterinary Officer, BVSc, MVS, Tick Fever Center, 280 Grindle Road, Wacol, Queensland, 4076, Australia

GENERAL INTRODUCTION: BABESIOSES

Introduction

Bovine babesiosis, or redwater as it is commonly known, is a tick-borne disease caused by the intra-erythrocytic protozoan parasite Babesia. A number of species are known to infect cattle: Babesia bovis,^{57, 65} B. bigemina,^{57, 65} B. divergens,¹⁹³ B. occultans,⁸⁸ B. major and B. ovata .¹¹⁷  They are widespread in tropical and subtropical areas, and are transmitted principally by ixodid Rhipicephalus (Boophilus) spp. ticks.¹⁰ Of these species, only Babesia bovis and Babesia bigemina are economically important⁶³ and therefore this chapter will focus on these two species. Babesia divergens occurs in Europe and is of zoonotic importance.¹⁹³ Characterisation of less important species, the tick vectors of some species and epidemiological significance are not always certain.^{75, 77, 65, 178} Babesia orientalis occurs in water buffalo (Bubalus bubalis),⁹⁰ but is not further considered here.

The acute disease is characterized by haemolysis, circulatory disorders in the case of Babesia bovis, and death may follow in some instances. Bos taurus breeds of cattle are particularly susceptible although the disease can also be economically important in Sanga and Bos indicus breeds. Clinically inapparent infections commonly occur in young animals, and recovered animals become latent carriers for variable periods. Recovery is followed by a lasting immunity to the infecting parasite. Cross-immunity between the two organisms is limited.
Babesia bovis was first reported in southern Africa in 1941¹⁴¹ although clinical evidence of its presence in South Africa was recorded as early as 1905.¹⁵⁷ It was probably introduced with the Asian blue tick Rhipicephalus (Boophilus) microplus during the latter part of the nineteenth century (see Vectors: Ticks).  Reports from Australia, Argentina and USA are also found in the late nineteenth and early twentieth century.¹⁶

Babesia bigemina is principally transmitted by R.(B.) microplus and by the common, indigenous African blue tick R. (B.) decoloratus. Babesia bigemina would therefore have been endemic in the subcontinent for centuries. Indeed, babesiosis is said to have been the cause of high cattle mortality in the present-day KwaZulu-Natal Province of South Africa prior to European settlement in the 1830s.⁶⁵

Several accounts have been published of the history of babesiosis and other tick-borne diseases in southern Africa and Australia, as well as of the people involved in the early battles against these diseases, and the impact on livestock industries. These reports are well worth reading.^{7, 91, 112, 170, 172, 181}

The impact of babesiosis in Africa in the early twentieth century was masked by a devastating East Coast fever epidemic (see East Coast fever). The campaign to control this epidemic by intensive regulatory control of the vector Rhipicephalus appendiculatus lasted half a century and had a big effect on the single-host Rhipicephalus (Boophilus) spp.., ensuring that babesiosis remained of secondary importance for many decades.

In the latter part of the twentieth century, relaxation or breakdown of tick control measures and the advent of acaricide resistance in Rhipicephalus (Boophilus) spp. caused babesiosis to increase in prevalence and significance to the point where it became recognized as one of the most important livestock diseases in southern Africa.^{13, 57, 65, 67, 113, 143}  (see Vectors: Ticks).

Although the diseases caused by Babesia bovis and Babesia bigemina are clinically very similar, it is important to separate them for a number of reasons. The names Asiatic (European) and African redwater, respectively, have come into common use in Africa. While Babesia bovis is the more virulent of the two parasites, Babesia bigemina is probably more important in southern Africa because of its wide distribution. In this review, however, we pay more attention to Babesia bovis, mainly because it has been studied more intensively, is much better understood than Babesia bigemina and is generally more important throughout the world.

Aetiology and life cycle

The genus Babesia belongs to the phylum Apicomplexa, class Sporozoasida, order Eucoccidiorida, suborder Piroplasmorina and family Babesiidae.^{6, 114, 115}  The Babesia spp. known to infect cattle, and their principal vectors and distribution, are listed in Table 1.

Table 1 Bovine Babesia spp. and their vectors (based on 16).